Self-starting synchronous electric motor



April 11, 1939. I A. B. pobuz 2,153,775

SELF*STARTING SYNCHRONOUS ELECTRIC MOTOR Filed March 15, 1936 E (1% I Z i 33 k 3 12 i 2Q E I /5 M g 7 I r /3 l6 l 1 [/zz en for flrt/zur 5. Poole By 2 r.

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Patented Apr. 11, 1939 UNITED STATES- 2.153.175 SELF-STARTING srNonaoNoUs anaemic Moron Arthur B. Poole, Bristol, Com, assignor to The E. Ingraliam Company, Bristol, Conn., a corporation of Connecticut Application March 13, 1936, Serial No. 68,674 g 5 Claims. (or. 172-278) This invention relates to an improvement in.

synchronous motors, and particularly to that type of synchronous motors which are self-starting and which are primarily designed for use in clocks, though available for other uses.

One of the objects of the present invention is to provide a superior self-starting synchronous electric motor characterized by minimum hum or other noise attributable to the movement of the rotor.

A still further object is to provide a superior self-starting synchronous motor having ample synchronous torque as well as starting torque. and characterized by the low mass of its rotor.

, A further object is to provide a synchronous motor of the class referred to, in which side-pull upon the rotor axis is minimized.

With the above and other objects in view, as will appear to those skilled in the art from the following, considered in conjunction with the accompanying drawing and appended claims, the present invention includes all features disclosed therein which are novel over the prior art.

In the accompanying drawing:

Fig. 1 is a view in rear elevation of a selfstarting synchronous electric motor constructed in accordance with the. present invention;

Fig. 2 is an edge view thereof Fig. 3 is a transverse sectional view taken on the line 3-4 of Fig. 1;

Fig. 4 is a perspective tachedf and Fig. 5 is a perspective view of one of the poleew of the rotor depiece plates detached.

The synchronous electric motor herein chosen for the illustration of the present invention in cludes two complementary laminated pole-pieces l and II, each of which is composed of a plurality (five, more or less) of corresponding polepiece plates l2- composed of iron, soft steel or othersuitable material. Each pole-piece plate l2 just referred to is laterally ofi'set at its lower end and is provided with an integral core-tang II as especially well shown in Fig. 5.

Each pole-pece l0 and II as thus composed of a group of corresponding pole-piece plates I2 is arranged in opposition so that the core-tangs I3 of each thereof extend in opposite directions through an energizing-coil ll. The free end of each of the saidcore-tangs is secured to the opposed pole-piece by the threaded rear ends of studs l having nuts l6 and each offsetting from a rear movement-plate IT. The energizing-coil I4 is provided with complementary leads I8 and I9 which may be connected to a suitable source of alternating current of commercial frequency.

The pole-piece I0 is provided at its upper end with an inwardly-extending polar-projection and is provided adjacent its inner end and hence adjacent the energizing-coil It with a polar-pro- I jection 2|. The polar-projection 2| constitutes an inturned extension of an arm 22 extending inwardly from the pole-piece III in a direction substantially concentrically with respect to a rotor 23. As will be seen by reference to Figs. 1 and 5 in particular the arm 22 of the pole-piece I0 is formed by notching the said pole-piece as at 2211' to thereby cause the flux-pathto the polar-proiection 2| to have substantially the same reluctance as the flux-path to the polar-proiection 20 before referred to.

Similarly, the pole-piece 'H is provided at its outer end with an inwardly-extending polarprojection 24 which is located substantially diametrically opposite the lower polar-projection 20 2| of the pole-piece I0. Diametrically opposite the polar-projection 20 of the pole-piece It the pole-piece II is formed with a polar-projection 25 formed at the inner end of an arm 26, which latter is created by suitably notching as at 21 the 25 pole-piece ll.

" Preferably and as shown, the polar-projection 20 of the pole-piece l0 and the polar-projection 24 of the pole-piece II are in contact or substantial contact and the latter polar-projection is encircled by a so-called shading-coil" 22 which together with a similar shading-coil .22 upon the polar-projection 2| oi' the pole-piece Ill serves to create a rotating-field effect. Similarly, the polar-projection 2| of the pole-piece ill 85 and the polar-projection 25 of the pole-piece ll are in contact or substantial contact as shown particularly well in Fig. 1. I

For the purpose of stabilizing the pole-pieces I 0 and II with respect to each other and to preto vent their vibrating under the influence .oi' the alternating flux supplied by the energizing-coil H. the outer ends of each of the said. polepieces are secured together by a pair of complementary tie-plates 3040 which are preferably 46 formed of brass or other non-magnetic mate rial. For a similar p rpose, the arms 22 and 26 of the respective pole-pieces l0 and II are rigid- 1y connected together by a tie-plate 3|.

As before described, the lower. portions of the 60 pole-pieces I 0 and I l are supported by the rear movement-plate I! by means of studs l5 and in a similar manner'transversely in line with the axis of the rotor 23 the said pole-pieces are secured by nuts 32 to the-rear ends of studs "-33 offsetting from the rear movement-plate H before referred to.

The rotor 23 is formed of relatively-thin transversely-flexible permanent-magnet material and is provided at intervals with radial slots 34 providing a plurality of flexible salient poles 35. Preferably, the said-rotor is of a thickness not less than .003 inch and not more than .010 inch though it has been found for the structure shown .006 inch is most satisfactory. Furthermore, it has been found that the rotor performs its function most satisfactorily with a carbon-content ranging from .9% to 1.1%.

As thus constructed, the rotor 23 is not only permanently magnetic but each of its salient poles ii is transversely flexible, whereby it operates in the field created by the pole-pieces l0 and H with reliable, synchronous and self-starting characteristics.

The rotor 23 is provided with a central bushing 36 which is mounted with a drive-fit upon the forward end of a shaft 31 extending forwardly from a. gear-case 38. The said gear-case rests against the rear face of the rear movementplate- I! before referred to and is held in such position by means of a retaining-yoke 39 mounted' at its respective opposite ends upon the studs "-33. The gear-case 38 may contain a suitable reduction gearing (not shown) serving to transpose the relatively-rapid speed of the rotor 23 into the relatively-slow motionof a drivepinion 00 mounted upon a drive-shaft 4| rearwardly extending from the said gearcase as shown particularly well in Figs. 2 and 3.

As is well known to designers of miniature self-starting synchronous electric motors, one of the most difficult problems to overcome in order to produce such motors upon a production basis is the problem of balancing the synchronous torque with'respect to the self-starting torque. Thus, if the lock-in tendency of the rotor is too strong, it will serve to prevent or retard the self-starting of the motor. On the other hand, if the self-starting torque is not properly related :to the synchronous or lock-in torque, the rotor will have a tendency to assume speeds above its intended synchronous speed.

By means of the present invention the amount of flux reaching the polar-projections adjacent the energizing-coil H is rendered substantially the same as the flux reaching the remote polarprojections, so that the reliable functioning of the motor is assured without undue side-pull upon the rotor and its shaft to the detriment of the bearings. It has been found, furthermore, that the transversely-flexible character of the rotor materially assists in preventing the lock-in tendency of the rotor from nullifying the self-starting torque afforded by the stator structure. All of the features cooperate in providing a selfstarting synchronous electric motor which is simple, reliable and eflective and which may be produced by mass-production methods.

.The invention may be carried out in other specific ways than that herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiment is therefore to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

I claim.

1. A self-starting synchronous electric motor, including in combination: a rotor having a plurality of salient poles, each of which is less than 0.010 inch thick and transversely flexible independently of the others; an energizing-coil; a pair of complementary pole-pieces respectively extending from the opposite ends of the said coil, each of the said pole-pieces being provided with a pair of polar-projections extending toward the said rotor, one polar-projection of a given polepiece being located adjacent the said coil, and the other polar-projection being located remotely therefrom and substantially diametrically opposite one of the polar-projections of the other pole-piece; one polar-projection of each of the said pole-pieces being shaded and located in substantial contact with the unshaded polar-projection of the other pole-piece.

2. A self-starting synchronous electric motor, including in combination: a rotor having a plurality of salient poles, each of which is less than 0.010 inch thick and transversely flexible independently of the others; an energizing-coil; a pair of complementary pole-pieces respectively extending from the opposite ends of said coil, each of the said pole-pieces being provided with a pair of polar-projections extending toward the said rotor, one polar-projection of a given polepiece being located adjacent the said coil, and the other polar-projection being located remotely therefrom and substantially diametrically opposite one of the polar-projections of the other pole-piece; one polar-projection 'of each of the said pole-pieces being shaded and located in substantial contact with the unshaded polarprojection of the other pole-piece; and each of the aforesaid complementary pole-pieces being shaped and proportioned to feed to its remote polar-projection flux of substantially the same density as is fed to its polar-projection which is adjacent the aforesaid energizing-coil.

3. A, self-starting synchronous electric motor, including in combination: a field-structure having an energizing-coil and polar-projections; and a rotor of permanent-magnet material posi tioned to be acted upon by the polar-projections of the said field-structure, and having a plurality of independently laterally-flexible salient poles of a thickness of less than 0.010 inch and spaced apart by slots which intersect the periphery of the rotor.

4. A self-starting synchronous electric motor, including in combination: a field-structure having an energizing-coil and polar-projections; and a rotor of permanent-magnet material positioned to be acted upon by the polar-projections of the said field-structure, and having a plurality of independently laterally-flexible salient poles of a thickness not more than 0.008 inch and not less than 0.003 inch and spaced apart by slots which intersect the periphery of the rotor.

5. A self-starting synchronous electric motor, including in combination: a field-structure having an energizing-coil and polar-projections; and a rotor of permanent-magnet material and positioned to be acted upon by the polar-projections of the said field-structure, and having a plurality of independently laterally-flexible salient poles of a thickness not more than 0.00? inch and not less than 0.005 inch am. spaced apart by slots which intersect the periphery of the rotor.

' ARTHUR B. POOLE. 

